A small number of consumers take excessive and potentially harmful amounts of dietary supplements, according to survey results announced by the Food and Drug Adminstration at a press conference last week.
Forty percent of Americans take vitamin and mineral supplements and many take doses that exceed the recommended dietary allowances (RDA) established by the National Academy of Sciences, says the report. The report, to be published in the Journal of the American Dietetic Association's December issue, is based on a random sample of 2,991 adults age 16 and older.
"This survey is the first national sample that provides information on the amount of nutrients being consumed," says Fred Shank, deputy director of the Office of Nutrition and Food Sciences at the FDA. "It focuses attention on certain nutrients that some consumers are getting at high enough levels to be a concern."
One of the most abused nutrients, according to the survey, is vitamin A. At proper levels, it aids night vision and growth of bones, skin, teeth and hair. But at five to 10 times the RDA, this vitamin, the eighth most commonly consumed nutrient, can be toxic. According to the study, 4 percent of supplement users ingest more than 25,000 international units (IU) of vitamin A daily, or five times the RDA. In high doses, vitamin A can cause birth defects, high pressures within the skull, headaches, dry skin, bone malformations, enlarged liver or spleen, loss of appetite and irritability.
The vast majority of supplement users take no more than five times the RDA for most vitamins and minerals, the survey found. But for eight vitamins (thiamine, riboflavin, vitamin C, pantothenic acid, vitamin E, vitamin B12, niacin and vitamin B6), consumers take between 10 and 50 times the RDA. The consequences of such doses are disputed.
"The RDAs are not the Ten Commandments," says Bonnie Liebman, nutrition director of the Center for Science in the Public Interest. "There's a lot of doubt and uncertainty surrounding the RDAs."
A panel assigned by the National Academy of Sciences to review existing RDA guidelines has been unable to agree on the new ones. Its report has been postponed indefinitely.
A vitamin-deficient diet can cause diseases such as beriberi, a vitamin B1 deficiency that damages the heart and kidneys, and rickets, a vitamin D deficiency characterized by bone deformaties. Today, however, experts are more concerned with the effects of high doses of dietary supplements.
Roughly 50 percent of supplement users take only one product, but 11 percent consume between five and 14 different dietary supplements, which are defined as any product containing one or more of 33 specific vitamins, minerals or "miscellaneous dietary components."
Shank is uncertain whether the FDA can act to regulate high doses. "Right now, the agency is looking at the possibilities to see if we can establish a maximum safe level of vitamin A," he says. "I don't know if we can establish that level. But I'm concerned that consumers may be encouraged to enhance their supplement consumption and push into toxic levels with some of these so-called nutrients." The push for more vitamins and higher doses comes from many places, according to experts, not the least of which is promotion from a $3 billion-a-year vitamin industry.
"In many cases, it's a little smidgen of science magnified by heavy marketing," says Liebman, who believes moderate doses of dietary supplements can be valuable. "The public isn't reading scientific literature, they're responding to Madison Avenue marketing.
"People think that if some is good, then more is better, and that they can't lose since they will excrete what their bodies don't need. This doesn't necessarily apply to extremely high doses."
Liebman, like many experts, advises against high doses. "You can develop imbalances," she says. "Taking too much zinc, for instance, can inhibit your copper absorption; too much iron can impair your zinc absorption. We just don't know the effects of high doses."
Liebman believes publicity explains why some nutrients are reported in the FDA's survey as being more widely used than others.
Vitamin C, considered by some to cure colds and cancer, is one of the most widely publicized nutrients. It is also the most widely consumed. Almost 91 percent of supplement users take vitamin C, either by itself or in combination with other vitamins and minerals, says the FDA report. Thiamine is the second most popular nutrient, followed by riboflavin, vitamin B12, vitamin B6, niacin, vitamin E, vitamin A and vitamin D.
While the use of dietary supplements is slightly more widespread among women than men, according to the FDA report, women also consume different nutrients. Several nutrients (thiamine, riboflavin, vitamin B12, vitamin B6, niacin and pantothenic acid) were most widely used by women. Men, however, consume more minerals, such as zinc, iodine, copper, magnesium and manganese.
The FDA survey also shows that supplement consumption is more common in the West than in the rest of the nation. The typical person taking dietary supplements is white, well-educated, and earning more than $25,000 annually, the survey says.
The FDA will begin collecting data in two months for a similar survey on dietary supplements.
The telephone interviews for this survey were conducted in 1980.
"We know there's been a little noise about the volume of dietary supplements in recent years, but the dollar volume of the industry is about the same," says Shank. "This information is still valuable. It presents a reasonable picture of what's happening."